1. Field of the Invention
The present invention relates to an insertion device for inserting a deformable intraocular lens into the eye. Examples of such a deformable intraocular lens include a deformable intraocular lens that is inserted into the eye in place of the natural lens when the latter is physically extracted because of cataracts, and a vision correction lens that is inserted into the eye for the sole purpose of vision correction.
2. Description of the Related Art:
Implantation of an intraocular lens for treating cataract has been widely performed since 1949, when Ridley implanted for the first time an artificial lens, i.e., intraocular lens into the human eye in place of an opaqued natural lens during cataract surgery.
The intraocular lens used first had an optical portion made of polymethyl methacrylate (PMMA). The implantation of the intraocular lens was accompanied by complications which occurred after the cataract surgery. Many ophthalmologists have shown interest in the complications and have studied them. As a result, most of the problems have been solved. However, since the optical portion is made of a hard material, an incision for implantation of such an intraocular lens must have a dimension somewhat greater than the diameter of the optical portion. Since an incision to be formed in the eyeball is large, in the degree of astigmatism after surgery increases due to suture of the incision.
A method of surgery has been pointed out as a cause of the above-mentioned complications. That is, the conventional surgery for extracting a natural lens because of cataract has been performed by using an ECCE (extracapsular cataract extraction) operation technique in which a lens is extracted without crushing it. Since this operation technique has required formation of an incision of about 10 mm, the operation caused astigmatism quite often. To solve this problem, a technique called pharmacoemulsification (PEA) using an ultrasonic emulsification/suction apparatus has been developed recently. In this method, an opaqued natural lens is crushed and emulsified using ultrasonic waves emitted from a cylindrical ultrasonic chip, and is sucked for extraction. When this method is used, the size of an incision formed in the eyeball can be decreased to a size sufficient for insertion of the cylindrical ultrasonic chip. A crushed lens can be extracted through an incision of about 3 to 4 mm. Therefore, this method makes it possible to perform the extraction operation by forming only a small incision, which mitigates the astigmatism after the operation. However, since the optical portion is made of a hard material, an incision for implantation of such an intraocular lens must have a dimension somewhat greater than the diameter of the optical portion, as mentioned above. In the case of a standard intraocular lens having an optical portion of 6.0 mm, an incision having a size equal to or greater than 6.5 mm must be formed. Therefore, even if an opaqued natural lens is extracted through a small incision using pharmacoemulsification, the incision must be widened so as to insert an intraocular lens. Accordingly, the problem of astigmatism occurring after surgery due to the large incision has not been solved.
In order to mitigate astigmatism after surgery, improved intraocular lenses have been developed which can decrease the size of incisions. Examples of such improved lenses include an intraocular lens having an oval optical portion which is inserted into an incision such that its smaller radius is oriented in the direction of the incision, and an intraocular lens with an optical portion having a reduced diameter. However, each of these intraocular lenses still has a hard optical portion. Therefore, employment of these intraocular lenses decreases the incision size only to about 5.5 mm (i.e., only by about 1 mm).
In order to solve the above-described fundamental problems, intraocular lenses themselves have been improved recently. Such an improved intraocular lens is disclosed in Japanese Patent Application Laid-Open (kokai) No. 58-146346. In the intraocular lens, at least an optical portion is made of a deformable elastic material having a predetermined memory characteristic. Alternatively, at least an optical portion is made of an elastic material having a predetermined memory characteristic, and supports are provided which are made of a material different from that of the optical portion and are adapted to support the optical portion within an eye. Moreover, as disclosed in Japanese Patent Application Laid-Open (kokai) Nos. 58-146346, 4-212350, 5-103803, 5-103808, 5-103809, and 7-23990 improved insertion tools have been proposed. Using these tools, the optical portion of an intraocular lens is compressed, rolled, bent, stretched, or folded so as to reduce its exterior size, thereby making it possible to insert the intraocular lens through a small incision. These intraocular lenses and insertion tools therefor make it possible to perform surgery by forming only a small incision, thereby mitigating astigmatism after surgery.
FIGS. 32 to 35 show the conventional deformable intraocular lenses. The deformable intraocular lens shown in FIG. 32 is composed of a circular optical portion 2 and two symmetrically disposed supports 3. The circular optical portion 2 is made of an elastic material having predetermined memory characteristics. The supports 3 are made of a material different from that of the optical portion 2, and the bases 3a of the supports 3 are embedded in the peripheral region of the optical portion 2 for fixing, while the wire-shaped tails 3b are curved. The optical portion 2 has on the periphery thereof projections 2a for reinforcing the positions where the bases 3a of the supports 3 are embedded. The deformable intraocular lens 1 shown FIG. 33 is configured in the same manner as is the deformable intraocular lens of FIG. 32 except that the projections 2a are omitted. Each of the deformable intraocular lenses shown in FIGS. 34 and 35 is composed of a circular optical portion 2 and a pair of thin plate-shaped support portions 4 that are integral with the optical portion 2. The optical portion 2, like the optical portion 2 shown in FIG. 32, is made of an elastic material having predetermined memory characteristics. The support portions 4 are projected from the periphery of the optical port 2 in opposite directions.
An insertion device disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 7-23991 is used for deformable intraocular lenses, as shown in FIGS. 32 to 35, each of which is composed of the optical portion 2 and the support portions 3 or 4, of which at least the optical portion 2 has predetermined memory characteristics. The deformable intraocular lens 1 is folded in order to reduce its exterior size and is advanced along an insertion tube having, for example, a cylindrical shape, in order to be inserted into the eye through an incision formed in the eyeball.
FIGS. 26(a), 26(b) and 27 show the structure and operation of the conventional insertion device. First, an enclosing member 5 of the insertion device having a hinge portion 6 is opened. A deformable intraocular lens is placed on a lens receiving section 7 such that the lens engages grooves 9a and 9b. Subsequently, the enclosing member 5 is closed so as to reduce the exterior size of the deformable intraocular lens and hold it. The grooves 9a and 9b become shallower toward the insertion-tube side of the lens receiving section 7. However, the grooves 9a and 9b extend up to the rear end of the lens receiving section 7 while maintaining constant depth. Since the grooves 9a and 9b converge at the front side with respect to the direction along which the lens is pushed out, the position where the lens is to be placed can be determined with reference to the converged portions. However, since the grooved structure continues unchanged to the rear end, no reference for positioning exists at the rear side, rendering the positioning difficult. Further, when the enclosing member 5 is closed, the deformable intraocular lens placed in the lens receiving section may move rearward.
After the operation of placing the intraocular lens on the lens receiving section 7 and closing the enclosing member 5, an engagement member 15 provided on a device body 12 is moved toward the lens receiving section 7, while the closed state is maintained, so that the engagement member 15 engages the enclosing member 5 to maintain the closed state thereof.
After completion of the entire operation for setting the lens, a push rod 13 of the insertion device is advanced to push forward the deformable intraocular lens received in the enclosing member 5. As a result, the deformable intraocular lens is inserted into the eye through the tip end of a insertion tube 11 provided at the front end of the enclosing portion, which tip end can be inserted into the eye through a small incision formed on the eye ball.
However, in the conventional insertion device, a hinge portion 6 projects outward with respect to the grooves 9a and 9b formed in the lens receiving section 7. Therefore, when a deformable intraocular lens is placed on the lens receiving section 7 having such a configuration, as shown in FIG. 30, the deformable intraocular lens 1 interferes with the hinge portion 6 and curves. If the deformable intraocular lens 1 is allowed to remain in such a state for a long period of time, the lens 1 deforms with time.
Accordingly, immediately before the lens is inserted into the eye the operation of placing the deformable intraocular lens must be performed quickly, and therefore, the lens cannot be placed on the lens receiving section 7 in advance. That is, before insertion of the deformable intraocular lens into the eye, there is always required an operation for placing the lens on the lens receiving section 7. Further, during the placement operation, the lens must be precisely placed at a proper position. However, the operation for precise and quick placement of the lens at a proper position is very difficult, because the intraocular lens and the lens receiving section 7 are both very small, resulting in the problem that an imprecise placement operation causes an insertion failure, such as abnormal insertion of the intraocular lens into the eye.
Meanwhile, insertion of a lens into the eye for the sole purpose of vision correction has recently been performed as an application of the above-mentioned intraocular lens insertion technique--which has been used for treatment of cataracts. For the vision correction purpose as well, there has been developed a lens in which at least the optical portion is formed of a deformable elastic material having predetermined memory characteristics, as in the intraocular lens for cataract treatment, in order to reduce the size of an incision. The above-described insertion device can be used when the deformable vision correction lens is to be inserted into the eye through a small incision.
That is, the above-described insertion device has enabled insertion of a deformable intraocular lens, such as a deformable intraocular lens for cataract treatment or a deformable vision correction lens, into the eye through a small incision.